Chair base



FIG. 1 is a perspective view of a chair base according to the present invention;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a top view thereof;

FIG. 5 is a bottom view thereof; and,

FIG. 6 is a side elevational view thereof, the opposite side being a mirror image.

The broken lines shown in the Figures are for environmental purposes only and form no part of the claimed design. 

The ornamental design for a chair base, as shown and described. 